Mitigation of fouling in refinery heat exchanger networks by optimal management of cleaning

A method for optimizing the cleaning schedule in large continuously operating heat exchanger networks (HENs) such as refinery crude preheat trains is presented. The method is based on two heuristics:  (i) discretisation of the operating horizon into a number of equally long periods in which cleaning decisions are allocated and (ii) solution of the resulting mixed integer nonlinear programming (MINLP) problem by a multiple starting point strategy and selection of the best locally optimal solution. The network performance equations are written in terms of the binary decision variables and are not linearized further, giving rise to a nonconvex objective function. The formulation includes constraints set by pumparound operation and pressure drop. Different deterministic relationships between pressure drop and fouling resistances are discussed. The form of the objective function is discussed, as a fixed horizon approach has a significant effect on the results obtained. Solution of the MINLP model is demonstrat...